Field of the Invention
The present invention relates to wireless communication and more particularly, a method for controlling transmission power of uplink control channel and an apparatus using the method.
Related Art
LTE (Long Term Evolution) is a standard for mobile communication and it is based on the 3GPP (3rd Generation Partnership Project) TS (Technical Specification) Release 8. LTE-A (Advanced) is a mobile communication standard representing a major enhancement of the LTE.
In the LTE system, ACK/NACK (acknowledgement/negative acknowledgement), which is used for checking reception of downlink data, can be transmitted through an uplink control channel. An uplink control channel supports several formats for this purpose.
Transmit Diversity (TxD) is one of techniques for transmitting ACK/NACK. Transmit diversity is the technique that transmits identical information through antenna ports different from each other. SORTD (Spatially Orthogonal Resource Transmit Diversity) is one implementation of TxD. SORTD is a technique that transmits identical information by using resources orthogonal to each other among different antenna ports.
ACK/NACK can also be transmitted by channel selection. Channel selection is a technique for representing ACK/NACK state by using resources selected from among a plurality of resources and a combination of modulation symbols transmitted through the selected resources.
Meanwhile, the LTE system determines transmission power of an uplink control channel when ACK/NACK is transmitted through the uplink control channel. Power offset values are determined differently for the respective formats of the uplink control channel depending on whether transmit diversity is applied for the corresponding format. When channel selection is employed for ACK/NACK transmission, transmit diversity is not taken into consideration. Therefore, the LTE system does not define a power offset value for the case where transmit diversity is applied for channel selection.
On the other hand, the LTE-A is considering applying transmit diversity for channel selection. Therefore, how to determine the power offset value for an uplink control channel turns into a problem for the case where channel selection and transmit diversity are both applied to the uplink control channel.